Synchronization channel structure for direct communications



|Project |IEEE 802.16 Broadband Wireless Access Working Group |

|Title |Supplementary Channel for Talk-around Direct Communications |

|Date Submitted |2011-09-20 |

|Source(s) |Jihoon Choi, Young-Ho Jung |E-mail: |

| |Korea Aerospace University |jihoon@kau.ac.kr, yhjung@kau.ac.kr |

| |Sungcheol Chang, Seokki Kim, Eunkyung Kim, Miyoung Yun, Won-Ik | |

| |Kim, Sungkyung Kim, Hyun Lee, Chulsik Yoon, Kwangjae Lim |scchang@etri.re.kr |

| |ETRI | |

|Re: |Call for Comments on the 802.16n AWD |

|Abstract |This provides AWD text proposals for supplementary channel structure of talk-around direct communications. |

|Purpose |To be discussed and adopted by 802.16 TGn |

|Notice |This document does not represent the agreed views of the IEEE 802.16 Working Group or any of its subgroups. It represents only the views of |

| |the participants listed in the “Source(s)” field above. It is offered as a basis for discussion. It is not binding on the contributor(s), who|

| |reserve(s) the right to add, amend or withdraw material contained herein. |

|Release |The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications |

| |thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may |

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| |Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802.16. |

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Supplementary Channel for Talk-around Direct Communications

Jihoon Choi, Young-Ho Jung

Korea Aerospace University

Sungcheol Chang, Seokki Kim, Eunkyung Kim, Miyoung Yun, Won-Ik Kim, Sungkyung Kim, Hyun Lee, Chulsik Yoon, Kwangjae Lim

ETRI

1. Introduction

A part of communication resources for infra-structure communication link can be assigned for TDC (talk-around direct communications) in IEEE 802.16n [1]. Using the assigned resources, multiple pairs of TDC links are provided based on OFDMA (orthogonal frequency division multiple access). The frame structure for TDC is proposed in [2]. The TDC frame is composed of synchronization channel, Sup-CH (supplementary channel), and dedicated channel.

In this contribution, we propose the details of Sup-CH structure for TDC in IEEE 802.16n. The Sup-CH is composed of ranging channel, CQI (channel quality indicator) channel, and feedback channel. We define the specific sequence for ranging channel and codeword set for CQI and feedback channels.

1 2. Proposed Sup-CH structure

[pic]

Figure 1. Proposed Sup-CH structure in the frequency domain

Figure 1 describes the proposed Sup-CH structure for TDC in the frequency domain. Details of the Sub-CH structure are defined in [2]. One Sup-CH is composed of four distributed mini-tiles, where a mini-tile denotes (2 subcarriers)((5 symbols) rectangular-shaped resources. A Sup-CH includes ranging channel, CQI channel, and feedback channel, which are transmitted in TDM (time division multiplexing) manner. The specific sequence for ranging channel and the codeword set for CQI and feedback channels are defined in the following sections.

1. Ranging channel

[pic]

Figure 2. Ranging channel structure in the frequency domain

When the Sup-CH is used to transmit the ranging channel, the ranging sequence is mapped to the Sup-CH resources as shown in Figure 2. {Sk; 0(k(7} denotes a binary sequence with length 8, defined by

[S0 S1 S2 S3 S4 S5 S6 S7] = [1,-1, -1,1, -1,1, 1,-1] (1)

The same binary sequence is repeatedly transmitted for 5 OFDM symbols. The ranging channel is periodically transmitted, where the starting slot number and the transmission period are determined during the link initialization for TDC. Using the ranging channel, the receiver can estimate time offset, frequency offset, link SINR (signal to interference plus noise ratio), etc. Also, the estimation accuracy can be improved by accumulating multiple ranging channels.

2. CQI channel

[pic]

Figure 3. CQI channel structure in the frequency domain

[pic]

Figure 4. Mapping of information in the CQI channel

The process of composing the CQI channel is illustrated in Figure 4. The CQI channel payload bits are used to generate the CQI sequence according to Table 1. The resulting bit sequence is modulated, repeated and mapped to the CQI channel symbols s[k] (0 mapped to +1 and 1 mapped to -1). The mapping of s[k] to the Sup-CH resources is defined as follows.

[pic] (2)

where Ki[j] denotes the j-th element of Ki , defined by

[pic] (3)

[pic] (4)

[pic] (5)

[pic] (6)

Table 1. Sequences for CQI channel

|Index |Sequence |Usage |

|0 |1111111111 |level 0 |

|1 |0010110001 |level 1 |

|2 |0100100110 |level 2 |

|3 |1001101000 |level 3 |

|4 |1011000100 |level 4 |

|5 |0110001010 |level 5 |

|6 |0000011101 |level 6 |

|7 |1101010011 |level 7 |

|8 |1100011000 |Reserved |

|9 |0001010110 |Reserved |

|10 |0111000001 |Reserved |

|11 |1010001111 |Reserved |

|12 |1000100011 |Reserved |

|13 |0101101101 |Reserved |

|14 |0011111010 |Reserved |

|15 |1110110100 |Reserved |

The codeword set defined in Table 1 can carry up to 4 information bits. The codeword set is mapped to the SINR level, determined by the AMS transmitting the CQI channel using the Ded-CH preamble and the pilot symbols included in the Ded-CH.

The CQI channel is periodically transmitted, where the starting slot number and the transmission period are determined during the link initialization for TDC. Since the ranging channel and the CQI channel are transmitted in TDM manner, the ranging channel and the CQI channel should be assigned to separate time slots, by properly adjusting the starting slot number and the transmission period.

3. Feedback channel

The Sup-CH can be assigned for feedback channel, that includes ACK (acknowledgement) channel, NAK (no ACK) channel, MCS (modulation and coding scheme) Change Confirm, RCHG (resource change) indication, etc. The feedback channel is transmitted using the slots which are not used by the ranging channel and the CQI channel. The feedback channel uses the same codeword set and symbol sequence to subcarrier mapping as the CQI channel.

The codeword sequences and mapping of feedback channel are defined in Table 2. When the data packet received at the Ded-CH is successfully decoded, ACK information is transmitted. When HARQ is used, the failure of data packet decoding is denoted as 4 kinds of NAK information corresponding to the HARQ frame number. The AMS transmitting data packets can transmit the MCS Change Command message considering the CQI level received from the Sup-CH. As a response to the MCS Change Command message, the MCS Change Confirm is transmitted. The AMS receiving data packets sends RCHG Indication to request the change of the Ded-CH in use.

Table 2. Sequences and mapping of feedback channel

|Index |Sequence |Usage |

|0 |1111111111 |ACK |

|1 |0010110001 |NAK for frame 0 |

|2 |0100100110 |NAK for frame 1 |

|3 |1001101000 |NAK for frame 2 |

|4 |1011000100 |NAK for frame 3 |

|5 |0110001010 |MCS Change Confirm |

|6 |0000011101 |RCHG Indication |

|7 |1101010011 |Reserved |

|8 |1100011000 |Reserved |

|9 |0001010110 |Reserved |

|10 |0111000001 |Reserved |

|11 |1010001111 |Reserved |

|12 |1000100011 |Reserved |

|13 |0101101101 |Reserved |

|14 |0011111010 |Reserved |

|15 |1110110100 |Reserved |

2 3. Simulation results for CQI and feedback channels

We perform numerical simulations in TDC environments to evaluate the CQI and feedback channels for various codeword sets. For fading channel generation, we developed a M2M (mobile-to-mobile) channel model by modifying the 802.16m EMD MIMO SCM (spatial channel model) described in [4] considering the M2M channel models proposed in [5] and [6]. The M2M channel model used in the simulation exploits the time domain power profile of the 802.16m EMD, and considers the mobility of the transmitter. Also, the spatial parameters for the transmitter have similar statistical characteristics with those for the receiver. Among the channel generation scenarios of the 802.16m EMD, we used the Bad Urban Macro NLOS channel.

In the simulation, we consider codeword sets with 3-bit, 4-bit, 5-bit, and 6-bit information. For comparison, IEEE 802.16m PFBCH (primary fast feedback channel) with 6-bit information is considered as well. The codeword set with 4-bit information is defined in Table 1, and codeword sets with 3-bit, 5-bit, 6-bit information are defined in Tables 3-5.

Table 3. Sequences for CQI and feedback channels (6-bit information)

|Index |Sequence |Index |Sequence |

|0 |1111111111 |32 |1111111100 |

|1 |1010101111 |33 |1010101100 |

|2 |1100111110 |34 |1100111101 |

|3 |1001101110 |35 |1001101101 |

|4 |1111001111 |36 |1111001100 |

|5 |1010011111 |37 |1010011100 |

|6 |1100001110 |38 |1100001101 |

|7 |1001011110 |39 |1001011101 |

|8 |1111110110 |40 |1111110101 |

|9 |1010100110 |41 |1010100101 |

|10 |1100110111 |42 |1100110100 |

|11 |1001100111 |43 |1001100100 |

|12 |1111000110 |44 |1111000101 |

|13 |1010010110 |45 |1010010101 |

|14 |1100000111 |46 |1100000100 |

|15 |1001010111 |47 |1001010100 |

|16 |1111111010 |48 |1111111001 |

|17 |1010101010 |49 |1010101001 |

|18 |1100111011 |50 |1100111000 |

|19 |1001101011 |51 |1001101000 |

|20 |1111001010 |52 |1111001001 |

|21 |1010011010 |53 |1010011001 |

|22 |1100001011 |54 |1100001000 |

|23 |1001011011 |55 |1001011000 |

|24 |1111110011 |56 |1111110000 |

|25 |1010100011 |57 |1010100000 |

|26 |1100110010 |58 |1100110001 |

|27 |1001100010 |59 |1001100001 |

|28 |1111000011 |60 |1111000000 |

|29 |1010010011 |61 |1010010000 |

|30 |1100000010 |62 |1100000001 |

|31 |1001010010 |63 |1001010001 |

Table 4. Sequences for CQI and feedback channels (5-bit information)

|Index |Sequence |Index |Sequence |

|0 |1111111111 |16 |1111111000 |

|1 |1010111101 |17 |1010111010 |

|2 |1100111110 |18 |1100111001 |

|3 |1001111100 |19 |1001111011 |

|4 |1111010101 |20 |1111010010 |

|5 |1010010111 |21 |1010010000 |

|6 |1100010100 |22 |1100010011 |

|7 |1001010110 |23 |1001010001 |

|8 |1111100110 |24 |1111100001 |

|9 |1010100100 |25 |1010100011 |

|10 |1100100111 |26 |1100100000 |

|11 |1001100101 |27 |1001100010 |

|12 |1111001100 |28 |1111001011 |

|13 |1010001110 |29 |1010001001 |

|14 |1100001101 |30 |1100001010 |

|15 |1001001111 |31 |1001001000 |

Table 5. Sequences for CQI and feedback channels (3-bit information)

|Index |Sequence |Index |Sequence |

|0 |1111111111 |4 |1111000011 |

|1 |1010101010 |5 |1010010110 |

|2 |1100110001 |6 |1100001101 |

|3 |1001100100 |7 |1001011000 |

In the simulation, the SNR (signal-to-noise ratio) is defined by

[pic] (5)

where PS is the per-subcarrier average power of TDC link and NS is the per-subcarrier noise power. Simulation parameters for signal generation and OFDMA operations are summarized in Table 6. Non-coherent detection is used for codeword decoding.

Table 6. Simulation parameters

|Parameter |Value |

|Carrier frequency |2.3 GHz |

|Bandwidth |10 MHz |

|FFT size |1024 |

|CP size |128 |

|Sampling rate |11.2 MHz |

|Number of transmit antennas |1 |

|Number of receive antennas |1 |

|Velocity of transmitter |30 km/h |

|Velocity of receiver |30 km/h |

|Moving direction of transmitter |(/6 |

|Moving direction of receiver |-(/4 |

|Timing offset |16 samples |

|Normalized frequency offset |0.02 |

Figures 3 and 4 show the BLER (block error rate) of CQI and feedback channels for various codeword sets in AWGN and fading channel, respectively. The Sup-CH for TDC uses 8 subcarriers for one codeword transmission, while IEEE 802.16m PFBCH uses 6 subcarriers per codeword. Therefore, the Sup-CH for TDC requires 1.25 dB SNR gain to achieve the same coverage as IEEE 802.16m PFBCH. The codeword set with 4-bit information exhibits 1.5 dB gain in AWGN and 1.7 dB gain in fading channel, compared to PFBCH with 6 bits. Therefore, using the codeword set with 4-bit information, the CQI and feedback channels for TDC have comparable or slightly better coverage than IEEE 802.16m PFBCH.

[pic]

Figure 4. Performance comparison in AWGN

[pic]

Figure 5. Performance comparison in fading channel

4. References

1] IEEE C802.16n-11/0051r2, “Dedicated resources allocation for direct communications in IEEE 802.16n,” March 2011.

2] IEEE C802.16n-11/0152xxx, “Frame structure for talk-around direct communications,” Sept. 2011.

3] IEEE Std. 802.16-2009, “IEEE Standard for Local and metropolitan area networks; Part 16: Air Interface for Broadband Wireless Access Systems,” May 2009.

4] IEEE 802.16m-08/004r5, “IEEE 802.16m evaluation methodology document (EMD),” Jan. 2009.

5] C. S. Patel, G. L. Stuber, and T. G. Pratt, “Simulation of Rayleigh-faded mobile-to-mobile communication channels,” IEEE Trans. Commun., Nov. 2005.

6] M. Patzold, B. O. Hogstad, and N. Youssef, “Modeling, analysis, and simulation of MIMO mobile-to -mobile fading channels,” IEEE Trans. Wireless Commun., Feb. 2008.

5. Proposed Text for the 802.16n Amendment Working Document (AWD)

Note:

The text in BLACK color: the existing text in the 802.16n Amendment Draft Standard

The text in RED color: the removal of existing 802.16n Amendment Draft Standard Text

The text in BLUE color: the new text added to the 802.16n Amendment Draft Standard Text

[-------------------------------------------------Start of Text Proposal---------------------------------------------------]

[Remedy1: Adapt the following change in Section 17.3.2.6 in the 802.16n AWD]

17.3.2.6 Talk-around Direct Communication

[note: This contribution provides text proposals for the following sections:

17.3.2.6.2.1 Frame structure

17.3.2.6.2.2 Synchronization channel

17.3.2.6.2.3 Dedicated channel

17.3.2.6.2.4 Supplementary channel]

17.3.2.6.2.4 Supplementary channel

[pic]

Figure xx1. Supplementary channel structure

Figure xx1 describes the proposed Sup-CH structure for TDC. Details of the Sub-CH structure are defined in 17.3.2.6.2.1. One Sup-CH is composed of four distributed mini-tiles, where a mini-tile has (2 subcarriers)((5 symbols) rectangular-shaped resource elements. A Sup-CH includes ranging channel, CQI channel, and feedback channel, which are transmitted in TDM (time division multiplexing) manner.

17.3.2.6.2.4.1 Ranging channel

[pic]

Figure xx2. Ranging channel structure

The ranging sequence is mapped to the Sup-CH resource elements as shown in Figure xx2. {Sk; 0(k(7} denotes a binary sequence with length 8, defined by

[S0 S1 S2 S3 S4 S5 S6 S7] = [1,-1, -1,1, -1,1, 1,-1]

The same binary sequence is repeatedly transmitted for 5 OFDM symbols. The ranging channel is periodically transmitted, where the starting slot number and the transmission period are determined during the link initialization.

17.3.2.6.2.4.2 CQI channel

[pic]

Figure xx3. CQI channel structure

[pic]

Figure xx4. Mapping of information in the CQI channel

The process of composing the CQI channel is illustrated in Figure xx4. The CQI channel payload bits are used to generate the CQI sequence according to Table yy1. The resulting bit sequence is modulated, repeated and mapped to the CQI channel symbols s[k] (0 mapped to +1 and 1 mapped to -1). The mapping of s[k] to the Sup-CH resource elements is defined as follows.

[pic]

where Ki[j] denotes the j-th element of Ki , defined by

[pic]

[pic]

[pic]

[pic]

Table yy1. Sequences for CQI channel

|Index |Sequence |Usage |

|0 |1111111111 |level 0 |

|1 |0010110001 |level 1 |

|2 |0100100110 |level 2 |

|3 |1001101000 |level 3 |

|4 |1011000100 |level 4 |

|5 |0110001010 |level 5 |

|6 |0000011101 |level 6 |

|7 |1101010011 |level 7 |

|8 |1100011000 |Reserved |

|9 |0001010110 |Reserved |

|10 |0111000001 |Reserved |

|11 |1010001111 |Reserved |

|12 |1000100011 |Reserved |

|13 |0101101101 |Reserved |

|14 |0011111010 |Reserved |

|15 |1110110100 |Reserved |

The codeword set defined in Table yy1 can carry up to 4 information bits. The codeword set is mapped to the SINR level, measured by the AMS transmitting the CQI channel using the Ded-CH preamble and the pilot symbols included in the Ded-CH. The CQI channel is periodically transmitted, where the starting slot number and the transmission period are determined during the link initialization. The ranging channel and the CQI channel shall be assigned to separate time slots, by properly adjusting the starting slot number and the transmission period.

17.3.2.6.2.4.3 Feedback channel

The Sup-CH can be used to transmit the feedback channel, that includes ACK channel, NAK channel, MCS Change Confirm, RCHG Indication, etc. The feedback channel is transmitted using the slots which are not used by the ranging channel and the CQI channel. The feedback channel uses the same codeword set and symbol sequence to subcarrier mapping as the CQI channel. The codeword sequences and mapping of feedback channel are defined in Table yy2.

Table yy2. Sequences and mapping of feedback channel

|Index |Sequence |Usage |

|0 |1111111111 |ACK |

|1 |0010110001 |NAK for frame 0 |

|2 |0100100110 |NAK for frame 1 |

|3 |1001101000 |NAK for frame 2 |

|4 |1011000100 |NAK for frame 3 |

|5 |0110001010 |MCS Change Confirm |

|6 |0000011101 |RCHG Indication |

|7 |1101010011 |Reserved |

|8 |1100011000 |Reserved |

|9 |0001010110 |Reserved |

|10 |0111000001 |Reserved |

|11 |1010001111 |Reserved |

|12 |1000100011 |Reserved |

|13 |0101101101 |Reserved |

|14 |0011111010 |Reserved |

|15 |1110110100 |Reserved |

[-------------------------------------------------End of Text Proposal----------------------------------------------------]

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